Such a type of buoy, often referred to as a life buoy, is aboard ships or aircrafts for use in an emergency so as to indicate the position of the survivors at sea or in the ocean. The life buoy of this type is equipped with a radar responder designed to have a transponder function, or to transmit respondent radio waves at the reception of radar waves transmitted from the searcher's radar on 9 GHz in common throughout the world. The radar responder transmits respondent radio waves at the same frequency as that of the searcher's radar. When the searcher's radar receives the reply from the responder of a life buoy, a continuous line of glittering dots are displayed on the screen.
To explain the system of the known life buoy more in detail, reference will be made to FIG. 1:
When the searcher's radar receives respondent radar waves 2 from a life buoy, a continuous line of glittering dots 3 are displayed on a screen 1, wherein the screen has a center 4 around which the dots 3 appear. When the life buoy receives the seacher's radar waves, it transmits respondent waves 2 which are swept at a time period of Ts several times in a range .DELTA.F of 9300 to 9500 MHz. The sweeping signals are received in the receptive band width Br, and are represented as glittering dots or spots 3.
In general, the life buoy must satisfy the following conditions:
(1) Regardless of any weather on the ocean radar waves can be effectively transmitted between the life buoy and the searcher;
(2) Without special techniques for which an official licence is required, the life buoy can be operated with ease;
(3) The life buoy must be compact, strong and inexpensive, without undesirably influencing its stability.
In addition, the life buoy must be maintained such that no failure occurs when an emergency happens. Particularly, special care must be taken not to cause the life buoy to operate when the ship is tossed about in stormy seas. The high pitch and roll of the ship provides a similar condition at which the operation of the life buoy is initiated in the emergency of its shipwreck. Accordingly, the life buoy must be constructed such that it can recognize between an emergency and a non-emergency, and if an emergency occurs, it must be sure to operate automatically when the buoy is thrown into the sea.
It is known in the art to employ a halved outer case for accommodating the responder, wherein the case is dividable by pulling a string coupled to the responder so as to allow the responder to be thrown on the water. This halved type of case is disclosed in Japanese Laid-Open Patent Specification No. 55-154482. It is also known in the art that a floating responder is equipped with an auto-responder adapted to respond to radar waves from a searcher, and additionally with a lamp which the survivor can use as a light for his convenience as well as a beacon for the searcher. This floating responder is disclosed in Japanese Laid-Open Patent Specification No. 55-152483.